Method for generating a hologram on a disc surface

ABSTRACT

A method for generating a hologram on a disc surface provides for the use of calibration spots burned onto a disc with an accuracy greater than one half wavelength of light.

FIELD OF THE INVENTION

[0001] The present invention relates generally to data storage disc anddisc drives for reading and recording data on data storage discs. Morespecifically, the invention relates to a method for generating ahologram on a data storage disc.

BACKGROUND OF THE INVENTION

[0002] Data storage discs, such as that shown at 10 in FIG. 2, store adiverse array of data including music, movies and educational material.Currently images stored on such data storage discs are only accessibleduring playback of the disc in an appropriate disc drive. Such imagesmay include logos, advertising and other images related to the data onthe disc, e.g., a data storage disc containing music data may, duringplayback, include images related to the music. Images related to thedata on the disc may also be displayed on packaging for the disc. e.g.,a data storage disc containing education materials may be packaged withimages related to the educational materials.

[0003] Meanwhile, holographic images (“holograms”) are currentlygenerated on a limited array of surfaces including glass, decals andfilms. In order to place a hologram on a non-film surface, the hologramis first generated on a film and then attached to the non-film surface.For example, to create a hologram on a plastic card, the hologram isfirst created on a film and then the film is attached to the card.

[0004] It would be desirable, therefore, to provide a method ofgenerating a holographic image on a data storage disc. It would furtherbe desirable to generate the image such that it is visible on the discsurface without requiring playback of the disc in a disc drive. It wouldfurther be desirable to generate the image directly on the disc surfacewithout requiring that the image be generated separately and thenattached to the disc.

SUMMARY OF THE INVENTION

[0005] The present invention relates to a method of generating ahologram on a disc surface. The method first provides for providing atleast one calibration spot on the first disc surface, positioned withinone half a wavelength of light. The method next reads the calibrationspot to determine positioning, and writes a set of hologram spots thatare representative of the hologram onto the disc surface at a differentlocation.

[0006] Another aspect of the invention provides for a computer programproduct for generating a hologram on a disc surface. The computerprogram product comprises means for providing at least one calibrationspot on the disc surface, positioned within one half a wavelength oflight. The computer program product further comprises means for readingthe calibration spot for positioning means for writing a set of hologramspots that are representative of the hologram onto a disc surface basedon position.

[0007] Yet another aspect of the invention provides for a system forgenerating a hologram on a first disc surface. The system comprises adisc surface that comprises at least one calibration spot positionedwith an accuracy of one half a wavelength of light. The system furthercomprises a disc-writing unit that comprises means for writing a set ofhologram spots that are representative of the first portion of thehologram onto a second disc surface based on the position of the atleast one calibration spot.

[0008] The foregoing forms as well as other forms, features andadvantages of the invention will become further apparent from thefollowing detailed description of the presently preferred embodiment,read in conjunction with the accompanying drawings. The detaileddescription and drawings are merely illustrative of the invention ratherthan limiting, the scope of the invention being defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 illustrates a top view of a first embodiment of opticaldisc in accordance with the present invention;

[0010]FIG. 2 illustrates a top view of an optical disc as known in theprior art;

[0011]FIG. 3 illustrates a block diagram of a preferred embodiment of acomputer system in accordance with the present invention;

[0012]FIG. 4A illustrates a side view of a first exemplary writing ofhologram spots onto a cross-sectional view of the optical disc of FIG.2;

[0013]FIG. 4B illustrates a top view of the optical disc of FIG. 2 aftera writing of a first set of hologram data as illustrated in FIG. 4A;

[0014]FIG. 5A illustrates a side view of a second exemplary writing ofhologram spots onto a cross-sectional view of the optical disc of FIG.2;

[0015]FIG. 5B illustrates a top view of the optical disc of FIG. 2 aftera writing of a second set of hologram data as illustrated in FIG. 5A;

[0016]FIG. 6 illustrates a top view of the optical disc of FIG. 2 aftera writing of a complete set of hologram data;

[0017]FIG. 7 illustrates a top view of a second embodiment of an opticaldisc in accordance with the present invention; and

[0018]FIG. 8 illustrates a side view of an exemplary writing of hologramspots onto the optical disc of FIG. 7.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0019]FIG. 1 illustrates an optical or data storage disc 40 inaccordance with one embodiment of the present invention. Disc 40 (“CD40”) may be, for example, a CDR, a CDRW, a DVD−R, a DVD−RW, a DVD+R, aDVD+RW, a DVDRAM, a DVDROM, and others as known in the art. CD 40 ofFIG. 1 may be compared with a prior art data storage disc 10 asillustrated in FIG. 2.

[0020] In addition, FIG. 1 shows a simplified three-dimensional image60. Image 60 may be, for example, a holographic image generated withconventional optical techniques or computational techniques. In such anoptical technique, a laser beam is split in two, with one part shiningdirectly at a large sheet of film and the other bouncing off the objectin question before being rejoined with the first beam on the film. Onthe film, the overlapping beams etch diffraction patterns that containenough information to render a reproduction of the light wavefront fromthe object recorded. This permits the entire image to be seen whenilluminated with a portion of the original wavefront (usually the beamcoming directly from the laser), which causes the full originalwavefront to be reproduced. Thus it can be viewed from different anglescreating the proper parallax effects, as in real life. When aholographic image 60 is viewed on the developed film, each eye sees aslightly different view of the image, providing the 3-D illusion. Thoseskilled in the art of hologram construction are familiar with techniquesfor reconstructing wavefronts. Those skilled in the art are furtherfamiliar with computing holograms by summing the rays of reflected lightto determine the diffraction pattern to create the desired hologram.Using the method of the current invention, the image 60 may be recreatedfrom the diffraction of incident light by carefully positioned dotsburned onto disc 40. The dots are burned onto the disk by a laser beamin a disk drive specifically designed to do so, which is the subject ofthis invention.

[0021]FIG. 2 illustrates a prior art data storage disc 10. Using amethod known in the art as constant linear velocity (“CLV”), a CD discdrive (“CD drive”) as known in the art decreases the rotation speed ofdisc 10 whenever reading data from the disc 10 or writing data to thedisc 10 in a direction from the center of disc 10 toward the perimeterof disc 10. Typically, a laser is used to heat the material along aspiral 11 that results in a formation of spots where the reflectivity tolight is different from that of the surrounding area 12. The presence orabsence of these spots along a conventional spacing on the spiral 11 isused to encode data to be stored on the disc 10. To facilitate thewriting of data, the disc 10 may include a conventionally stamped spiral11 (sometimes also called a pre-groove) extending from a center of thedisc 10 to the perimeter of the disc 10. The spiral 11 has a slightcontinuous wobble whereby a signal is modulated on the frequency of thewobble. The signal indicates the current position along spiral 11 and isused as a calibration signal to control the motor spinning the disc 10so that a CLV is maintained while writing data on the disc 10. Thisprimary information modulated onto the wobble of the track is known asthe Absolute Time In Pre-groove (ATIP). The signal may also indicateadditional information, which informs the drive about the optimumwriting parameters for the kinds of materials used in the recordabledisc 10. Using the ATIP, the motor control can spin the disc 10 at theproper angular rate so that a constant and relatively predictablevelocity is maintained while following the prestamped spiral 11. Thusthe proper data capacity of disc 10 can be ensured (the spiral 11 is notused up too fast because of too high a velocity, or the spots creatingthe spiral 11 are not too close to each other due to too low a velocity.Neither the signal encoded in the wobble, nor the wobble itself isrequired for reading data stored on the disc 10. The CD recording drivewill emit a laser beam to read modulation information on the spiral 11whereby the CD drive can calculate the position of the write head alongspiral 11.

[0022] However, the positioning information provided by the ATIP is muchmore coarse than one half of the wavelength of light, and thus is notsufficient to accurately control the burning of dots on the disk to forma viewable hologram.

[0023] Returning now to FIG. 1, the disc 40 of the present inventionalso comprises a spiral 41 spiraling from a center of optical disc 40 tothe perimeter of the optical disc 40.

[0024] Not only may this spiral 41 be used to facilitate the reading andwriting of data as conventionally described above, but the spiral 41 mayalso be used to reproduce holographic image 60 onto the surface ofoptical disc 40. In order to recreate image 60 on the surface of opticaldisc 40 in accordance with the present invention, a plurality ofcalibration spots 42 are formed along any portion of spiral 41 by anyknown technique. Preferably, the calibration spots 42 are stamped alongthe spiral 41 on the outermost revolution (“the last revolution”) of thespiral 41. The accuracy of the positioning of the calibration spots 42is such that the position along the entire spiral can be determined withaccuracy better than one-half of a wavelength of light. The calibrationspots 42 could also be placed elsewhere, for example closer to thecenter, but they would need to be more accurately placed to achievesufficient accuracy across the entire disk and might require the use ofa higher frequency laser to achieve that accuracy. Furthermore, therevolutions of the spiral are accurately stamped from the innermostrevolution to the outermost at predictable radial distances accurate toat least one half of the wavelength of light. Thus the radial distanceand angular position can be sufficiently accurately determined over theentire writing surface of the disk.

[0025] Holograms may be thought of as a complex diffraction grating,which diffract light in a way that constructively interferes to form awavefront representative from light reflected from a three dimensionalscene. One can think of a hologram as a statistical process where manydiffraction points are arranged such that the constructive interferenceof the light diffracting from these points, form the image desired whileall other interferences combine to leave a noise level much lower thanthe signal of the desired image. Thus, if diffraction points could beplaced at the proper places on a surface such as a CD 40, then ahologram of image 60 could be written on a CDR or other recordabledigital disc. Those skilled in the art of hologram writing willappreciate the benefits attendant to calculating the hologram prior towriting the hologram spots so that the precalculated data may be simplyaccessed during writing, rather than calculated during writing thehologram spots. However, the invention is practicable if the hologram iscalculated during the writing, but the speed may be limited by theprocessing power of the computer used. Those skilled in the art willalso appreciate the benefits attendant in viewing the hologram createdwith the invention under optimized conditions. The optimized conditionsmay include the use of lighting that has a sharp spectral peak, orpossibly viewed with a laser. Those skilled in the art will alsoappreciate that some applications may benefit from the use of a volumedielectric layer filter encapsulated with the disc to selectively filterall but a predetermined, desirable frequency of light, while filteringthe light in such a way that the light is permitted to pass from aselectively preferred direction so that most of the viewing light energycontributes to reconstructing the hologram. A selectively preferreddirection may include a direction perpendicular to the disc.

[0026] As further seen in FIG. 1, the pits in a prerecorded CD can serveas diffraction points. A diffraction point can be a place where light isreflected with greater amplitude or lesser amplitude than thesurrounding area. It can be a point where the light is phase shiftedwithout changing the reflectivity. Any of these are sufficient alone orin combination as a tool to create a hologram. In a recordable CD, theplaces where the laser alters the reflectivity of the surface are called“spots”. The CD provides a spiral track on which diffraction points canbe placed selectively such that they would provide the requireddiffraction of light to form a hologram of image 60. A writing of spotsrepresentative of the hologram onto the CD 40 requires a precision ofone-half the wavelength of light, or smaller, in ascertaining thewriting position of a write head whereby a proper positioning of thespots along the spiral 41 can be achieved.

[0027] As illustrated in FIG. 2, the typical prior art CD 10 has aspiral 11 with a wobble. More specifically, and as is known to thoseskilled in the art, the radial position of the track wobbles with a peakto peak wobble spacing of 50 to 60 micrometers along the track, and thiswobble represents the carrier signal for the frequency modulated ATIPsignal. Thus the wobble of spiral 11 cannot serve as a basis for aproper positioning of the spots used to recreate the hologram since thetypical spiral 11 does not offer the precision described above duringthe time that the spots are being written onto the CD 10. Additionally,the CLV rotation of CD 10 during writing of the spots onto CD 10 is notrepeatedly accurate from track-to-track of CD 10. Consequently, thespots can be placed in a track-to-track dithered position far exceedingthe bit size. This is detrimental to a reproduction of a hologram 60,because a nature of hologram requires an accurate positioning of thespots on CD 10 due to the required summation of light constructivelyinterfering from the spots. If a spot is more one half wavelength oflight from its intended position, the diffracted light will be out ofphase from its intended phase and source position, thus destructivelyinterfering with the intended image or contributing to the noise level.

[0028] However as FIG. 1 and FIGS. 3 through 7 illustrate, the method ofthe present invention provides a method that enables the generation ofholographic image 60 on a data storage disc.

[0029] In FIG. 3, computer hardware 20 is illustrated in accordance withone embodiment of the present invention. As shown in FIG. 3, computerhardware 20 includes a bus 21 for facilitating electrical communicationamong one or more central processing units (CPU) 22, a read-only memory(ROM) 23, a random access memory (RAM) 24, an input/output (I/O)controller 25, a disc controller 26, a communication controller 27, anda user interface controller 28.

[0030] Each CPU 22 is preferably one of the Intel families ofmicroprocessors, one of the AMD families of microprocessors, one of theMotorola families of microprocessors, or one of the various versions ofa Reduced Instruction Set Computer microprocessor such as the PowerPCchip manufactured by IBM. ROM 23 permanently stores various controllingprograms such as the Basic Input-Output System (BIOS) developed by IBM.RAM 24 is the memory for loading an operating system and selectivelyloading the controlling programs.

[0031] Controller 25 is an aggregate of conventional controllers forfacilitating an interaction between CPU 22 and pointing devices such asa mouse 30 and a keyboard 31, and between CPU 22 and output devices suchas a printer 32 and a fax 33. Controller 26 is an aggregate ofconventional controllers for facilitating an interaction between CPU 22and storage devices such as a hard drive 34, an optical drive 35, and afloppy drive 36. The hard drive 34 stores a conventional operatingsystem, such as, for example, IBM's AIX operating system or Microsoft'sWindows. Controller 27 is an aggregate of conventional controllers forfacilitating an interaction between CPU 22 and network 37. Controller 28is an aggregate of conventional controllers for facilitating aninteraction between CPU 22 and a graphic display device such as amonitor 38, and between CPU 22 and an audio device such as a speaker 39.

[0032] Those having ordinary skill in the art will appreciate additionalcomponents that may be included within computer hardware 20 inaccordance with the principles of the present invention. Those havingordinary skill in the art will also appreciate embodiments of thepresent invention alternative to computer hardware 20 for implementingthe principles of the present invention.

[0033] In FIG. 4A, an exemplary writing of a plurality of hologram spots43 onto the optical disc 40 is illustrated. The optical disc drive 35(FIG. 3) includes an optical laser 35 a capable of emitting light beamsto concurrently read data and write data from optical disc 40.Ordinarily, reading and writing operations on an optical disk start fromthe center and follow the spiral outward to the perimeter. Although thisinvention may be implemented using the center to perimeter direction,more accuracy may be achieved by starting at the periphery and followingthe track toward the center. This would require spinning the disk in theopposite direction from the one conventionally used. Indeed, it may bepreferred to write from the periphery of disc 40 to the center of disc40 to capitalize on the potentially greater accuracy afforded by thisstrategy.

[0034] For purposes of brevity, however, only the embodiment of a methodwriting from the periphery to the center is described. Similar methodswill be immediately recognizable to those of ordinary skill in the artfor writing a holographic image from the center of the disc 40 to theperiphery. The optical laser 35 a is aligned with the last revolution ofthe spiral 42 and an adjacent inner revolution of the spiral 43 (“thenext revolution”) to facilitate a concurrent reading of the calibrationspots in track revolution 42 and writing of the hologram spots in trackrevolution 43 onto the optical disc 40. Thus, the spots on the priorrevolution provide calibration information for writing spots on thefollowing revolution. As the spots are written, their precise locationsare remembered for use in computing the writing position in thefollowing revolution. From the reading of the calibration spots 44, theoptical disc drive 35 ascertains the positions of the calibration spots44 and writes the hologram spots 45 along the second revolution with apositioning corresponding to the reading of the positions of thecalibration spots 44 (i.e., a positioning of the hologram spots 45 toequal to or less than one-half a wavelength of light). The result is thewriting of hologram spots 45 as illustrated in FIG. 4B with a properpositioning to accurately contribute to the wavefront produced by theentire hologram. In some cases, hologram spots are not written atparticular places on the disc 40, depending on the original image 60.For example, location 46 on the disc 40 may be free of hologram spots45. From the reading of the calibration spots 44, the optical disc drive35 ascertains the positions of the calibration spots 44 and may also beable to determine the areas 45 along the second revolution wherehologram spots 45 will not be placed.

[0035] In one embodiment of the invention, the holographic image 60 isprecalculated into a series of locations that indicate where spotsshould be written along the spiral of the disk. The calibration spotsserve to provide accurate angular information about where the laser head35 a is positioned along the spiral. When it is in a position where aspot should be written, it does so. The position is calculated in polarcoordinates using r the radial distance from the center that isdetermined by the revolution number of the spiral and angle φ that isthe angular position determined using the calibration dots. The radialdistance can be accurately known by simply counting the revolutionsbecause the spacing of the pregroove spiral tracks can be reliably andrepeatably determined by the mold used in the manufacturing process ofthe disk.

[0036] For example, the image 60 may be translated into a sequence ofcommands which indicate to laser 35 that a hologram spots 45 should beplaced at coordinates (r₁,φ₁), (r₂,φ₂), . . . , (r_(n),φ_(n)) whichlocate points along the spiral 41 at which to write spots. Thecoordinates of these points correspond to places on the spiral where theconstructive interference from the image wavefront for image 60 exceedsa specified threshold. At other coordinates, no spot is written. Inaccordance with the present, invention, hologram spots 45 may also beplaced onto the surface of disc 40 based on previously placed hologramspots. For example, hologram spot 49 may be placed in relation tohologram spots 45 rather than in relation to calibration spots 44.Again, image 60 may be precalculated into a series of locations thatindicate where the spots 45, 49 should be placed. For example, image 60may be translated into commands that indicate to laser 35 that hologramspot 45 is to be written at coordinate (r_(m),φ_(m)). This coordinate isdetermined by knowing the coordinates of prior track spots 44, 45 usinginterpolation computations.

[0037] In FIG. 5A, an exemplary writing of a plurality of hologram spots45 onto the optical disc 40 continues. As the method proceeds from thefirst steps illustrated in FIGS. 4A and 4B where the optical disc isaligned with the first revolution, the laser 35 a moves along spiral 41.The optical laser 35 a is aligned with the second revolution of thespiral 41 and an adjacent inner revolution of the spiral 41 (“the thirdrevolution”) to facilitate a concurrent reading of the hologram spots 45and writing of the hologram spots 47 onto the optical disc along thethird revolution. From the reading of the calibration spots 44, theoptical disc drive 35 ascertains positions of the hologram spots 45. Thehologram spots 47 being placed along the third revolution having apositioning corresponding to the reading of the positions of thehologram spots 45 (i.e., a positioning of the hologram spots 47 to equalto or less than one-half a wavelength of light). The result is thewriting of hologram spots 47 as illustrated in FIG. 5B with a properpositioning to accurately project a portion of the hologramcorresponding to the hologram spots 47. Alternatively, the positioningof hologram spots 47 may be based in relation to calibration spots 44 asdescribed above at FIG. 4A.

[0038] As illustrated in FIG. 6, the method may proceed so that theoptical laser 35 a is aligned with the third revolution of the spiral 41and an adjacent inner revolution of the spiral 41 (“the fourthrevolution”) to facilitate a concurrent reading of further hologramspots and so on along the fifth revolution, the sixth revolution, etc.This read/write process is continued for the remaining revolutions ofthe spiral 41 whereby the result is a set of properly positioned spotsfor the entire hologram onto the optical disc 40. FIG. 6 illustratesthat, when the method of the present invention is completed, arecreation 65 of image 60 is written on the surface on disc 40. Therecreation 65 will also be a complete holographic image. FIG. 6 picturesthe method in its last iteration, i.e. on the innermost revolution ofspiral 41.

[0039] The size and positioning of the calibration spots 42, thehologram spots 43, the hologram spots 46 and hologram spots 47 wereillustrated above scale for the purposes of facilitating anunderstanding of the present invention. Those having ordinary skill inthe art will appreciate the actual size and the one-half wavelength oflight positioning of the calibration spots 42, the hologram spots 43,the hologram spots 46, and the hologram spots 47 is typicallyundetectable by the human eye. Additionally, those having ordinary skillin the art will appreciate that each calibration spot 42, each hologramspot 43, each hologram spot 46, each hologram spot 47 and other hologramspots not shown as well as the positioning may be undetectable forvarious reasons, such as, for example, dust on optical disc 40. As such,the optical disc driver 35 is operated to interpolate a positioning ofhologram spots being written when a reading of the calibration spots 41or a reading of previously written hologram spots involves a failure todetect one or more of the spots. In one embodiment, a phased-lock looptechnique is implemented to time the positions of each spot being readwhereby the optical disc driver 35 can maintain the detected timing whenfailing to detect one or more of the spots. Those having ordinary skillin the art will further appreciate that interpolation by the opticaldisc driver 35 is required when the hologram spots 43, the hologramspots 46, and the hologram spots 47 and other hologram spots not shownhave a spacing between pairs of spots that by design exceed one-halfwavelength of light.

[0040] In FIG. 7, an optical disc 50 is illustrated in accordance withone embodiment of the present invention. As shown in FIG. 7, tofacilitate the reading and writing of data, the optical disc 50 includesone or more annular rings of calibration spots such as, for example, anannular ring of calibration spots 51, an annular ring of calibrationspots 52, and an annular ring of calibration spots 53. Preferably, thecalibration spots 51, the calibration spots 52, and the calibrationspots 53 are stamped on the optical disc 50 by any known technique withthe positioning of the calibration spots 51, the calibration spots 52,and the calibration spots 53 being equal to or less than one-half of awavelength of light. These additional annular rings of calibration spotscan reduce the drift in accuracy that might occur when simply using onlythe first calibration marks.

[0041] In FIG. 8, an exemplary writing of hologram spots onto theoptical disc 10 is illustrated. The optical disc drive 35 (FIG. 2)includes a hub holding mechanism 35 b and a motor 35 c. The hub holdingmechanism 35 b securely and stably holds the optical disc 10. The motor35 c is mechanically coupled to the hub holding mechanism 35 b and theoptical disc 50 to thereby synchronize a rotation of the optical disc 10and the optical disc 50. As the optical disc 10 and the optical disc 50are rotated, a write head 35 d conventionally emits light beams to writethe hologram spots (not shown) on the optical disc 10 and a read head 35e conventionally emits light beams to read the calibration spots on theoptical disc 50 (not shown) (e.g., calibration spots 53 illustrated inFIG. 7). From the reading of the calibration spots on the optical disc50, the optical disc drive 35 ascertains the position of the calibrationspots and writes the hologram spots on the optical disc 10 with apositioning corresponding to the reading of the positions of thecalibration spots (i.e., a positioning of the hologram spots to equal toor less than one-half a wavelength of light). The result is the writingof hologram spots on the optical disc 10 with a proper positioning ofspots to accurately project a hologram corresponding to the hologramspots on the optical disc 10. The optical disc driver can selectivelyemploy an interpolation as previously described herein of thecalibration spots on the optical disc 50. The addition of a separatecalibration disk adds cost to the device due to the extra laser head butincreases accuracy greatly. The hub mechanism 35 b should be designed tohold the optical disc 10 with sufficient firmness so that the disc doesnot slip in its angular position. In addition, the acceleration anddeceleration of spinning the disc should be controlled to minimizechance of slipping, and thus minimize the change of losing calibration.The calibration disc 50 could be implemented as a cylinder or in anynumber of other configurations. Disc 10 will still require at least onecalibration mark so that its initial angular relationship with respectto disc 50 can be known and so that the exact revolution number ofgroove 41 can be known.

[0042] Although the figures above illustrate the recreation of aholographic image onto a conventional optical disc, the method of thepresent invention may also be used to recreate a holographic image ontoother suitable surfaces. For example, an image may be created onto aglass disc. Alternatively, an image may be recreated onto the surface ofa film. In one embodiment of the invention, the film may then be adheredto another surface, such as, for example, the surface of an opticaldisc. Other embodiments of the invention may involve writing thehologram spots in three dimensions on the volume of the disc to createmore diffraction points and provide self-filtering for incidentlighting.

[0043] While the embodiments of the invention disclosed herein arepresently considered to be preferred, various changes and modificationscan be made without departing from the spirit and scope of theinvention. The scope of the invention is indicated in the appendedclaims, and all changes that come within the meaning and range ofequivalents are intended to be embraced therein.

What is claimed is:
 1. A method of generating a hologram on a first discsurface, comprising: providing at least one calibration spot on thefirst disc surface; reading the calibration spot to ascertain thecalibration spot positioning; and writing a first set of hologram spotsonto a second disc surface based on the calibration spot positioning,the first set of hologram spots being representative of a first portionof the hologram.
 2. The method of claim 1, wherein the first discsurface and the second disc surface are the same surface.
 3. The methodof claim 1 wherein the calibration spot comprises a plurality ofcalibration dots on the first disc surface, further comprising: writingthe first set of hologram spots onto the first disc surface based on thecalibration spot positioning, the first set of hologram spots beingrepresentative of the first portion of the hologram.
 4. The method ofclaim 1 wherein the first surface is a glass surface with the hologramon the surface, further comprising: writing a first set of hologramspots onto the second disc surface based on the calibration spotpositioning, the first set of hologram spots being representative of thefirst portion of the hologram.
 5. The method of claim 1 wherein thefirst surface and the second surface comprise matching calibrationspirals.
 6. The method of claim 1, further comprising: reading the firstset of hologram spots on the second disc surface to ascertain a firstset positioning; and writing a second set of hologram spots onto thesecond disc surface based on the first set positioning, the second setof hologram spots being representative of a second portion of thehologram.
 7. The method of claim 1, further comprising: interpolatingthe writing of the first set of hologram spots when the calibration spotpositioning exceeds one-half a wavelength of light.
 8. The method ofclaim 1 wherein the calibration spot has a calibration spot positioningthat is equal to or less than one-half a wavelength of light
 9. Acomputer program product for generating a hologram on a first discsurface, comprising: means for providing at least one calibration spoton the first disc surface, wherein the calibration spot has acalibration spot positioning that is equal to or less than one-half awavelength of light; means for reading the calibration spot to ascertainthe calibration spot positioning; and means for writing a first set ofhologram spots onto a second disc surface based on the calibration spotpositioning, the first set of hologram spots being representative of afirst portion of the hologram.
 10. The program of claim 9, wherein thefirst disc surface and the second disc surface are the same surface. 11.The program of claim 9 wherein the calibration spot comprises aplurality of calibration dots on the first disc surface, furthercomprising: means for writing the first set of hologram spots onto thefirst disc surface based on the calibration spot positioning, the firstset of hologram spots being representative of the first portion of thehologram.
 12. The program of claim 9 wherein the first surface is aglass surface with the hologram on the surface, further comprising:means for writing the first set of hologram spots onto the second discsurface based on the calibration spot positioning, the first set ofhologram spots being representative of the first portion of thehologram.
 13. The program of claim 9 wherein the first surface and thesecond surface comprise matching calibration spirals.
 14. The program ofclaim 9, further comprising: means for reading the first set of hologramspots on the second disc surface to ascertain a first set positioning;and means for writing a second set of hologram spots onto the seconddisc surface based on the first set positioning, the second set ofhologram spots being representative of a second portion of the hologram.15. The program of claim 9, further comprising: means for interpolatingthe writing of the first set of hologram spots when the calibration spotpositioning exceeds one-half a wavelength of light.
 16. A system forgenerating a hologram on a first disc surface, comprising: a first discsurface, wherein at least one calibration spot is disposed on the firstdisc surface, the calibration spot having a calibration spot positioningthat is equal to or less than one-half a wavelength of light; adisc-writing unit, wherein the disc-writing unit comprises means forwriting a first set of hologram spots onto a second disc surface basedon the calibration spot positioning, the first set of hologram spotsbeing representative of a first portion of the hologram.
 17. The systemof claim 16 further comprising: a disc-reading unit, wherein thedisc-reading unit comprises means for reading the calibration spot toascertain the calibration spot positioning.
 18. The system of claim 16wherein the disc-writing unit further comprises means for reading thecalibration spot to ascertain the calibration spot positioning.
 19. Thesystem of claim 16 wherein the calibration spot is pre-stamped into thefirst disc surface.
 20. The system of claim 16 wherein the disc-writingunit is a laser.
 21. The system of claim 16, further comprising: a hubholding mechanism for holding the first disc surface in relation to thesecond disc surface.